Abstract: The objective was to study the antioxidant activities and the antibacterial activities to bacteria,yeasts and molds of essential oil from Citrus medica. The antioxidant activities of essential oil from Citrus medica were evaluated based on the method of vitro antioxidant and agar diffusion. The results for the antioxidant capacity of essential oil from Citrus medica increased with the increasing concentration,there were scavenging capacity on DPPH free radicals,·OH free radicals( IC50= 0.32 mg / m L) and H2O2( IC50= 148 μg / m L). The antimicrobial activity and its stability of the essential oils against five species of microorganisms( Escherichia coli,Staphylococcus aureus,Bacillus subtilis,Saccharomyces cerevisiae,Aspergillus niger) were discussed by the disc diffusion method. The essential oils showed inhibition zones against all microorganisms tested. The data indicated that Aspergillus niger was the most sensitive microorganism tested with the largest inhibition zone( 25.39 ± 1.12) mm,and Staphylococcus aureus exhibited the smallest inhibition zone( 14.04 ± 1.35) mm. Minimum inhibitory concentrations ranged from 0.31~1.25 mg / m L.At the certain range of p H( 5 ~7),temperature( 80,115,121 ℃) and ultraviolet rays( 20,40 min) impact compared with the control,essential oil from Citrus medica remained relatively stable antimicrobial properties. The essential oil displayed a broad antimicrobial spectrum and exerted a strong antimicrobial effect against five strains tested.